Flattening The Curve With Hornady’s 6mm ARC

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Has Hornady cooked up the ultimate long-range AR cartridge in its new sexy-six, the 6mm ARC?

What Exactly Is The 6mm ARC:

• It is essentially a commercial version of the 6mm PPC.
• Though, it has a slightly larger case capacity of 34 grains of water.
• Given it's designed for AR-15 platform, its maximum average pressure is 52,000.
• Its forte is long-range and outperforms nearly all other popular AR-15 cartridges in this arena.

If you consider the evolution of the rifle, the goal has always been—and remains—to shoot with extreme precision, as far as possible, while experiencing the least recoil and influence from wind and gravity. Just look at the evolution of .30-caliber rifle cartridges; we went from the .30-30, to the .30-06, to the .300 Winchester Magnum and now to the .300 PRC. The desire to overcome the adverse effects of wind and gravity push the design of cartridges and bullets, and shooters relish every advancement no matter how minute. So, when someone argues that we don’t need a new rifle cartridge, what they’re essentially saying is that there’s nothing to be created that’ll be desirable or useful.

Well, that’s clearly not true. The enhancement of external ballistics has been the driving force behind cartridge creation since Louis-Nicolas Flobert’s 6mm parlor guns of the mid-1800s. Everyone wants to shoot harder, faster and flatter, so desire and utility clearly exist. This is particularly true of devotees of the AR-15. Both amateur and professional ballisticians have been trying to develop cartridges for that platform for a long time. Some of these cartridges, like the 300 Blackout, found great appeal. Others, like the .30 Remington AR, proved to be misunderstood. The latest attempt at extending the reach of the AR-15 is from Hornady, and it’s called the 6mm ARC.

According to Hornady, they identified a need for an “unnamed” Department of Defense entity and a concept cartridge was discussed. The entity showed extreme interest, so Hornady began development. Ultimately, the result of that collaboration is what’s now known as the commercially available 6mm ARC (Advanced Rifle Cartridge), which was adopted by that undisclosed government body. For what it’s worth, I’ve been fed the “secret government agency” line so many times that it means nothing to me. And, truth be told, it should mean even less to you. I don’t care if Carlos Hathcock himself divined his dream cartridge from upon high down to some engineer in the basement of Hornady; a cartridge either fills a desire and provides utility—or it doesn’t.

But, Why The 6mm ARC?

What exactly is the 6mm ARC? It’s indeed a new SAAMI (Sporting Arms and Ammunition Manufacturer’s Institute) approved cartridge. That means there exists a set of parameters and design specifications for ammunition and firearms manufacturers to follow when building ammunition or guns for it. This is critical, because for a cartridge to have any chance for commercial success it must be SAAMI approved. Otherwise, manufacturers avoid it like a Covid-infected anti. However, the 6mm ARC isn’t really as new as it might seem.

Along about 1975, Dr. Louis Palmisano and Ferris Pindell took the .220 Russian case, which was based on the 7.62x39mm Soviet cartridge and necked it up to 6mm (0.244 inch), and they also changed the shoulder angle to 30 degrees. The cartridge was explicitly created for benchrest shooting and, in fact, developed a winning reputation. Ironically, even though the 6mm PPC never gained SAAMI approval, it found great popularity in the benchrest competition circuit where most shooters made their own brass and loaded their own ammo. It should be noted, however, that there are several versions of the 6mm PPC. Though they’re minutely different, this is a result of a cartridge not having SAAMI approval.

While some believe the 6mm ARC is based on the 6.5 Grendel cartridge, it’s really nothing more than yet another variation of the 6mm PPC. No doubt, the 6.5 Grendel was some inspiration for the 6mm ARC project, and it could be argued the 6.5 Grendel is nothing more than a necked-up 6mm PPC. Of course, since bullet diameter is the primary distinguishing feature of any cartridge, this makes the 6mm ARC a closer relative to the 6mm PPC. Case capacity of the 6mm PPC is about 33 grains of water. Case capacity of the 6mm ARC is 34 grains. The most critical difference is that in bolt-action rifles, from which the 6mm PPC is typically fired, according to the Western Powders Handloading Guide, the 6mm PPC is loaded to pressures approaching 60,000 psi.

For the purposes of slowing extraction and extending bolt life, Hornady set the maximum average operating pressure (MAP) of the 6mm ARC at 52,000 psi. This is identical to the SAAMI MAP of the 6.5 Grendel, but 3,000 psi less than that of the .223 Remington and .224 Valkyrie. This makes perfect sense for Department of Defense applications, where extremely high round counts are expected. Soldiers and civilians want their guns to last as long as possible, and less pressure equals less wear and a longer life.

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So, How’s The 6mm Shoot?

Of course, I’m sure some shooters couldn’t care less about where a cartridge came from or his ancestral background. Most are interested in the ballistic performance and advantages it might offer over other cartridges. After all, like has already been established, harder hitting, faster flying and more gravity-defying cartridges have forever been the focus of cartridge and ammunition development. It matters not so much where and why we now have the 6mm ARC, what does matter is what it can do.

It gets tricky when you try to compare the external ballistic performance of various cartridges. This is partly because there are so many variables to consider. It’s even more complicated when the cartridges being compared are of a different caliber. So, let’s set the table for a proper comparison.

The 6mm ARC was designed for the AR-15 platform. Can it be fired in a bolt-action rifle? Sure. And, I’m sure we’ll soon see bolt-action rifles chambered for it. However, since the faster-shooting 6mm Creedmoor or .243 Winchester won’t work in an AR-15, it’d make no sense comparing the 6mm ARC to either. What’s offered here is a comparison of the 6mm ARC to other current SAAMI-approved cartridges that are AR-15 compatible.

There are a variety of ways to make this comparison. We could look at muzzle velocity and energy, and trajectories, and we could obtain this data from advertised ballistics or actual testing. Since the problem the 6mm ARC was created to solve was that of long-range performance, comparing muzzle velocities is mostly a waste of time. By the same token, comparing actual chronographed velocities is, too; it’s not unusual to see drastic velocity variations from one rifle to the next. So, we’ll compare advertised velocities in conjunction with data obtained from a ballistics program to look at a prediction of long-range performance.

Hornady Precision Hunter 6mm ARC 103 Grain $49 at Optics Planet

If we do that, we see that the best performing 6mm ARC load—the Hornady ELD Match load— will take 2.04 seconds to travel 1,200 yards. The best factory 6.5 Grendel load will take 2.26 seconds to travel the same distance, and the .224 Valkyrie gets there in 2.15 seconds. The best load for the .223 Remington—the original chambering for the AR-15—takes about 2.36 seconds to travel 1,200 yards. This is what you might call definitive proof that the 6mm ARC is the best AR-15 cartridge at defying gravity and wind. This is possible due to the muzzle velocity of the cartridge and the high ballistic coefficient (BC) of the bullets Hornady loads for it. The ELD Match bullet has a BC of 0.536 and the ELD-X bullet’s BC is 0.512.

Hornady Match 6mm ARC 108 Grain $39 at Optics Planet

Due to these high BC bullets used by Hornady, the 6mm ARC not only retains velocity, it also retains energy. At distance, it’ll hit harder than the other three cartridges. The bullets will also remain supersonic at greater distances. If you’re a lover of the AR-15 and have been wanting to extend your effective range, this is all good news. However, keep in mind these comparisons were based on advertised velocities, which begs the question of what you can expect out of a 6mm ARC in the real world.

Testing Theory

To find out, I acquired a 6mm ARC from Wilson Combat; it was their Super Sniper model with an 18-inch barrel. The Hornady ELD-X and ELD match loads were tested form this rifle and delivered average muzzle velocities of 2,711 and 2,661 fps, respectively. Hornady advertises these loads at 2,750 fps for the ELD Match load and 2,800 fps for the ELD-X load. Out of the Wilson Combat Super Sniper, both loads clocked in at 89 fps less than advertised. If Hornady’s advertised velocities were, as most advertised velocities are, based on a 24-inch barrel, this equates to a very reasonable 14.8 fps loss in velocity for each inch of barrel loss.

For argument’s sake, let’s just assume that the actual chronographed velocities from an 18-inch barrel are all you can ever expect to get out of the 6mm ARC from any barrel length. If those velocities are plugged into the ballistics calculator and compared to the advertised—not actual—muzzle velocities for the .223 Remington, .224 Valkyrie and 6.5 Grendel, the 6mm ARC still outperforms all three cartridges at 1,200 yards. This means the 6mm ARC is indeed the flattest-shooting commercial cartridge option out of the AR-15. This places it well within the definition of need, making it both desirable and damned useful.

It should also be mentioned that the Wilson Combat Super Sniper rifle delivered, as you might very well expect, fine precision. For five, five-shot groups at 100 yards, the ELD Match load averaged 1.046 inches and the ELD-X load 0.693 inch. How does that stack up against other AR cartridges? Based on my records and all the AR-15 rifles and cartridges I’ve tested over the years, average 100-yard precision is slightly more than 1.5 inches. So, not only is the 6mm ARC flat shooting, it can also deliver precision.

What’s it good for and will it hang around very long? Distance is its forte and with its 2020 introduction and ability to flatten the trajectory curve, the 6mm ARC might ought to have been called the “Corona cartridge.” If you want to shoot at distance with your AR-15, this is the cartridge.

I also predict that it’ll indeed be with us for a while, and not just in the AR-15 platform. It’s essentially a commercial version of the 6mm PPC so look for bolt-rifles to spring up soon. Well, at least as soon as this current ammunition and firearms buying spree subsides. Until then, you can pick up an AR-15 or a new upper chambered for the 6mm ARC and have an AR that shoots flatter than you ever imagined possible.

Editor's Note: This article originally appeared in the December 2020 issue of Gun Digest the Magazine.